Electron discharge device



ep 30,1947 P. w. STUTSMAN 2,428,048

ELECTRON DISCHARGE DEVICE Original Filed May 6, 1944 s Sheets-Sheetiv 6'll T X Sept. 30, 1947 P. w. STUTSMAN 2,428,048

ELECTRON DISCHARGE DEVICE OrigifiaIFiled may s, 1944 s SheetS-Shet 2SIG/VHL IMPuT 3/ MP l l l' v GHTHODE CONDENSER VOLT GE Sept. 30, 1947 wP, w. STUTSMAN 2, ,0

' I ELECTRON DISCHARGE DEVICE Original Filedfm 6, 1944 s Sheets-Sheet 56 519 T E/fY c/r/r/cnL 26! 617/0 Vuhqar.

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Patented Sept. 30, 1947 ELECTRON DISCHARGE DEVICE Paul W. Stutsman,Needham, Mass, assignor, by

mesne assignments, to Raytheon Manufacturing Company, Newton, Mass, acorporation of Delaware Griginal application May 6, 1944, Serial No.

534,494. Divided and this application September 15, 1945, Serial No.616,548

2 Claims.

This is a division of applicants copending application Serial No.534,494, filed May 6, 1944.

This invention relates to an electrical system utilizing a gaseousdischarge relay tube which conducts current between a cathode and anodein response to a predetermined Value of signal voltage applied to acontrol grid or electrode.

An object of this invention is to devise such a tube and system having ahigh grid impedance and which operates reliably with very low gridpower.

Another object is to devise such a tube and system which operatesconsistently under variable anode voltages with a substantially uniformmaximum required signal voltage of the order of about one volt.

A further object is to devise such a tube and system which operates froma source such as a battery with a very low standby current of the orderof a few micro amperes.

The foregoing and other objects of this invention will be bestunderstood from the following description of an exemplification thereof,reference being had to the accompanying drawings wherein:

Fig. 1 is a vertical cross-section of one form of my novel tube for usein my novel system;

Fig. 2 is a cross-section taken along line 2-2 of Fig. 1;

Fig. 3 is a circuit diagram of one embodiment of my novel system;

Fig. 4 is a set of curves illustrating the stand by conditions in thesystem of Fig. 3; and

Figs. 5 and 6 are characteristic curves of a tube built and operated inaccordance with my invention.

The tube as illustrated in Figs. 1 and 2 comprises a sealed glassenvelope l containing a glow discharge cathode 2, an anode 3, and a pairof cathanode grids 4, i disposed on opposite sides of a control grid 5.The envelope l is filled with a suitable ionizable gas at a substantialpressure. For example, a mixture of krypton and xenon at about mm. ofmercury may be utilized.

The cathode 2 is supported by a plurality of conducting support rods 5sealed in the upper end of a press 1 formed on the reentrant stem 8 ofthe envelope i. The cathode 2 may be made of a ribbon of a nickel alloyand coated with barium carbonate fused onto said ribbon in air at apressure of about 5 mm. of mercury. One of the conducting rods 6 may beprovided with a lead-in conductor 9 extending through the press I andaffording an external electrical connection to the cathode.

The grids 4 and 5 are preferably made of a relatively fine mesh ofnickel wire. The anode 3 may also be made of a disc of nickel. Ifrelatively small voltages are used between the cathode and anode, theelectrodes 3, E and .5 may be made of bright nickel. Under theseconditions, voltages of about the order of I45 volts or less may beused. However, where higher voltages are present, it is desirable thatthe surface of the electrodes 3, 4 and 5 be coated with a poorelectron-emissive material. Thus these electrodes are preferablycarbonized by being coated with a layer of finely divided carbon. Theelectrodes 3, 4 and 5 are each in the form of a flat disc supportedbetween a pair ofinsulating washers it. Each of these insulating washersis provided with a central opening H was to create an electron dischargepassage between the cathode 2 and the anode Ii. The insulating washersit are clamped together by a plurality of hollow rivets I2 which thusbind the assembly of the electrodes 3, 4 and 5 together into a compactunit. This unit is supported on the 'reentrant stem 8 by means of a pairof wire standards l3 sealed in the press l. The upper ends of thestandards i3 may be welded to two of the rivets l2. Each of thecathanode grids 4 has welded thereto a conducting table which in turn isWelded to a conducting rod M likewise sealed in the press l and providedwith an external lead-in conductor H5. The rod M, as it projects abovethe press I, is surrounded by a glass sleeve It so as to protect saidrod l4 against undesirable discharges. The glass sleeve [6 fits snuglyinto correspondin openings in the insulating washers ill. The controlgrid 5 likewise has welded thereto a conducting tab which in turn iswelded to a conducting rod 11 likewise sealed in the press I andprovided with an external lead-in conductor IS. The rod I1 is alsosurrounded by a glass sleeve l9 fitting snugly into correspondingopenings in the washers Ill. The purpose of the sleeve i9 is similar tothat described in connection with the sleeve I6. In order to cut. offall discharge paths between the electrodes except through the dischargeopenings ll in the washers ll), an additional insulating washer 2!] isplaced over the top of the electrode assembly and is provided with asingle central opening for the purpose of enabling an electricalconnection to be made to the anode 3. However, the washer 20 covers the.openings in the washers Ill through which the sleeves I6 and i9 3project and also covers the upper ends of the rivets l2. The washers Iand also the washer 20 fit snugly Within the side walls of the envelopeI, the washer 20 being retained in place by coming into contact with thelower portion of the upper curved section of the inner Walls of saidenvelope. The anode 3 has welded to its upper surface a. conducting stub2| to which is welded a flexible lead-in conductor 22. This lead-inconductor is sealed through the top of the envelope l and is connectedto an external connector cap 23 cemented to the top of said envelope.

As is well known, if two electrodes in an ionizable gas are broughtcloser together, the voltage at which the gas breaks down and at which adischarge is initiated between said electrodes falls until apredetermined distance is reached at which said breakdown voltage is aminimum. This distance is known as the minimum breakdown distance. Ifthe separation between the electrodes is decreased still further, thevoltage at which breakdown occurs is increased: In the presentarrangement the cathode 2 is preferably spaced from the lower cathanodegrid 4 by substantially the minimum breakdown distance. Since thecathode 2 is made of a ribbon having a substantial width, it will beseen that if any substantial part of the active surface of the oathode 2is at the minimum breakdown distance from the lower cathanode grid 4,breakdown at the minimum voltage value will occur between saidelectrodes. The anode 3 is spaced from the upper cathanode electrode 4by a distance substantially less than the minimum breakdown distance.The spacing between the electrode and each of the adjacent grids 4 ispreferablysubstantially the same as that of the spacing of the anode 3from the upper grid 4. In a practical case with the above-mentionedkrypton Xenon mixture at mm.-, the cathode was spaced about .040" fromthe lower grid 4, while the spacings between the electrodes 3, 4 and 5were each about .015".

The tube described above may be utilized in a circuit such as thatillustrated in Fig. 3, wherein the same reference numerals are appliedwhere the elements are identical with those of Figs. 1 and'2. In thiscircuit the cathode 2 is connected by its conductor 9 to ground. Theanode 3 is connected through a suitable load 25, a conductor 26,

and a source of potential 2'1, such as a battery, to ground. The battery2l' is polarized so as to make the anode 3 positive with respect to itscathode. The battery 2'5 is also connected through the conductor 25, acathanode resistance 29, and a cathanode condenser so to the groundconductor 9. The cathanode 4 is connected by means of its conductor I5to a point intermediate the resistance 29 and the condenser 30. A signalinput voltage may be supplied to the primary winding 3| of a signaltransformer 32 having a secondary winding 33. One end of said secondarywinding is connected through a condenser 34 to the conductor l8 leadingto the control grid 5. The other end of said secondary winding 33 isconnected by a conductor 35 to the conductor l5 connected to thecathanode l. A leakage grid resistance 35 is connected between theconductors l8 and I5.

During the standby condition, in which no signal voltage is supplied tothe primary winding 31, the operation of the system illustrated in Fig.3 is illustrated by the curves of Fig. 4. Under these'conditions,relaxation oscillations will be generated between the cathode 2 and theoathanode 4. These said relaxation oscillations are the result of theperiodic charging and discharging of the condenser 30. The curve a inFig. 4 represents the manner in which the voltage on condenser 38 variesduring such charging and discharging. This voltage rises along saidcurve a until a point a: is reached when the voltage between the cathode2 and the cathanode 4 is at its breakdown value. Thereupon an ionizingdischarge is initiated between said electrodes and the condenser 30 isdischarged by the resulting flow of current between said electrodes.Thus, when the discharge is initiated at the point :r, a current impulseb will fiow between the oathode 2 and the cathanode 4. Due to the flowof the current impulse b, the voltage on the condenser 30 falls asindicated by the point a beyond the curve :B. When this voltage falls toa value less than that which is sufhcient to maintain the discharge, thecurrent I) decreases to substantially zero and the discharge between thecathode 2 and the cathanode 4 is extinguished. Thereupon condenser 30 isrecharged and the cycle is repeated. The cathanode resistance 29 issufficiently large so that the charging current to the condenser 39remains at a substantially uniform value. This charging current In. isrepresented by the curve 0 in Fig. 4., The current Ika, is the standbydrain which the battery 21 is called upon to deliver. In a practicalcase this standby current has been about 25 micro amperes. This value isso small that the drain on the battery is negligible and its shelf lifeis in nowise decreased thereby.

With the present device only a very small bias on the grid 5 is requiredto prevent'a discharge from being propagated to the anode 3. A typicalcharacteristic curve of the grid 5 is shown in Fig. 5 in which the valueof D. 0. grid bias voltage required to prevent a discharge to the anode3 is shown with various values of voltage of the battery 2'! and.various values of capacity of the cathanode condenser 30. Values of gridvoltage more positive than those ndicated will cause a discharge to bepropagated to the anode 3. V

In the circuit of Fig. 3 the grid 5, due to the presence of the highleakage grid resistancetli, will assume a negative bias sufficient tohold off the anode discharge under conditions ;of' zero signal voltage.The electron flow to the grid 5 to maintain said negative bias is onlyabout .2 micro ampere in a practical case.

If a signal voltage is applied to primary winding 3!, this signalvoltage will be transferred through the transformer 32 and the condenser34 and the grid 5. When the signal voltage swings in a positivedirection so as to move the potential of the grid 5 more positive thanthe critical grid voltage, as shown for example in Fig. 5, electrons ofsufiiciently high speed projected into the space between the cathanodegrids 4, 4 will be caused to pass in sufiicient numbers to the anode 3to initiate a self-sustaining discharge between the anode 3 and itscathode 2. As will be explained below, such projection of electronsoccurs primarily at the beginning of each of the cathanode currentimpulses b as shown in Fig. 4. When the flow of current is initiated tothe an ode 3 the self-sustaining discharge which takes place ispropagated throughout the entire discharge path between the cathode 2and the anode 3. This causes the voltage drop between the cathanode dand the cathode 2 to fall to substantially the normal glow dischargevalue and thereafter the voltage drop persists at this value. Un-

der these conditions, the relaxation oscillations will be suppressed andthe device continues to operate with a substantially steady discharge,for example, of the order of five milliamperes between the cathode 2 andthe anode 3. In order to restore the circuit to its standby condition,it would be necessary to interrupt the flow of current in this circuitat least momentarily as by opening a switch 31 in the circuit leadingfrom the battery 21. A typical operating characteristic curv of the grid5 is shown in Fig. 6 in which the critical R. M. S. value of signalvoltage necessary to fire the tube is shown with various values for thecapacity of the cathanode condenser 30 and for various values of thegrid resistance 36.

The effectiveness and reliability of the tube and the system asdescribed above, are due, I believe at least in part, to the stabilizingof the tube con ditions by the relaxation oscillations. The breakdown ofthe discharge space between the cathode 2 and the cathanode 4 tends tooccur always at the same voltage, which voltage is dependent upon thegas, its pressure, the conditions of the surface of the cathode 2, andthe spacing between the cathode 2 and the cathanode 4. Thus, the actualvoltage of the battery 21 may vary over wide limits and still thevoltage on the cathanode will rise along the curve a (Fig. 4), and thecathanode space will break down at substantially the same peak value cc.It also appears that the speed at which the electrons from the cathanodspace are projected into the space between the cathanode grids l, 4 is aprimary controlling condition in so far as the control exerted betweenthe control grid 5 and the initiation of conduction to the anode 3 l areconcerned. During the non-conducting portion of the relaxationoscillation cycle, substantially no electrons are projected into thespace between the cathanode grids 4, 4 and any electrons which do enterthis space are of relatively low speed. When, however, the gap betweenthe cathode 2 and the cathanode 4 breaks down, the discharge is rapidlypropagated between said electrodes and substantially at that instant,electrons are projected through the lower cathanode grid 4 atsubstantially the maximum voltage attained by the cathanode 4 withrespect to the anode 3. Thereafter the speed of the projected electronsfalls ofi substantially as indicated by the falling portion of the curvea beyond the point r in Fig. 4. As already indicated the value of thecathanode voltage at the point a: is fixed by the tube constants andthus it will be seen that the critical control voltage is fixed largelyby said tube constants and varies over a relatively small range withadditional circuit variations. The most important variation in circuitconditions which is met with in practice is the variation of the batteryvoltage due, for example, to the aging of the battery. The extent towhich the critical grid voltage is independent of such battery voltages,is typically illustrated in Fig. 5. In this figure it will be seen thatwith various capacities for the cathanode condenser 30, the batteryvoltage may vary from 140 to 180 volts and yet the critical grid voltageremains below about one volt.

From the foregoing it will be seen that a tube and system, constructedand operated in accordance with my invention, satisfy the objects ofthis invention to a remarkable degree.

r type of cathode.

Of course it is to be understood that this invention is not limited tothe particular details as described above as many equivalents willsuggest themselves to those skilled in the art. For example, instead ofusing a source of direct current to energize the system and interruptingthe anode discharge by a switch 31, the tube could be made toperiodically discharge a condenser, or the anode voltage could be apulsating or alternating voltage and in this way the anode dischargewould be automatically interrupted in a periodic manner. Certainprinciples of this invention might likewise be utilized in a system inWhich the glow discharge cathode is replaced by a thermionic Variousother equivalents will suggest themselves to those skilled in the art.It is accordingly desired that the appended claims be given a broadinterpretation commensurate with the scope of the invention within theart.

What is claimed is:

1. An electrical space discharge tube comprising a sealed envelopecontaining an ionizable gas at a substantial pressure, a glow dischargecathode having an active surface, a foraminous cathanode electrodedisposed adjacent said cathode at a distance substantially equal to theminimum breakdown distance from a substantial portion of the activesurface of said cathode, a foraminous control electrode on the oppositeside of said cathanode electrode from said cathode, an auxiliaryforaminous electrode on the opposite side of said control electrode fromsaid cathanode electrode, and an anode on the opposite side of saidauxiliary electrode from said control electrode, said cathanodeelectrode, control electrode, auxiliary electrode and anode being spacedfrom each other by distances each substantially less than said minimumbreakdown distance.

2. An electrical space discharge tube comprising a sealed envelopecontaining an ionizable gas at a substantial pressure, a glow dischargecathode having an active surface, a foraminous cathanode electrodedisposed adjacent said cathode at a distance substantially equal to theminimum breakdown distance from a substantial portion of the activesurface of said cathode, a foraminous control electrode on the oppositeside of said cathanode electrode from said cathode, an auxiliaryforaminous electrode on the opposite side of said control electrode fromsaid cathanode electrode, an anode on the opposite side of saidauxiliary electrode from said control electrode, said cathanodeelectrode, control electrode, auxiliary electrode and anode being spacedfrom each other by distances each substantially less than said minimumbreakdown distance, and means for blocking off all discharge pathsbetween said electrodes except through the foramina of said cathanode,control and auxiliary electrodes.

PAUL W. STUTSMAN.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 1,962,159 Le Van June 12, 19342,072,637 Jobst Mar. 2, 1937

